Linear accelerator



Aug. 13, 1957 G. R. MARNER ET AL LINEAR ACCELERATOR' Filed Aug. l, 1951 Dls TAArcf Raul/l L, McCRfA/Qr BY Gflvf H MARA/fk Arron/rrr United States Patent lO 2,802,965 LINEAR ACCELERATOR Gene R. Manier, ,Iowa City, andARalph L. McCreary,

Cedar Rapids, Iowa, assignors to Collins Radio Cornpany, Cedar Rapids, Iowa, a corporation of Iowa Application August 1, 1951, Serial No. 239,724

3 Claims. (Cl. S15-5.16)

This invention relates ingeneral to accelerators` for chargedparticles and in particular to a particle accelerator of a new and novel type.

In the field of nuclear physics, it is oftentimes desirable to accelerate a charged particle to an extremely high' energy level. One method of doing this is with alinear accelerator wherein driving oscillators are connected to accelerating plates mounted linearly so as to accelerate the charged particles between each plate. Much energy is lost in coupling the energy to the driving plates and it' is an object of thepresent invention toffprovid'e anaccele'rating cavity which comprises the output cavity ofan electronic high-frequency tube.

Another object of` this invention is to provide a particle'- accelerator wherein-a iirst cavity resonator furnishes a beam of-energy to a-secondcavity resonator at a low voltage point so as to obtain voltage amplification at the maximum voltage point of the second cavity.

A further object of this invention is to provide an input cavity resonator which may be operated in Class C fashion to drive an output cavity resonator so as to obtain voltage amplification.

Yet another object of this invention is to provide a compact and easily manufactured particle accelerator.

A feature of this invention is found in the provision for a first resonant cavity which is formed with a direct current insulated grid structure so that it may be operated in Class C fashion and which shoots a beam of charged particles into the contines of a second resonant cavity at a position offset from the high voltage point of the second cavity; an injection system supplies a pulsed input to the second cavity at a high voltage point phased so as to be accelerated by the input from the rst cavity.

Further objects, features and advantages of this invention will become apparent from the following description and claims when read in view of the drawing, in which:

Figure 1 is a sectional view of the accelerator of this invention illustrating the input and output resonant cavities, and;

Figure 2 is a graph of voltage versus distance from the edge of the second resonant cavity.

Figure 1 illustrates an input resonant cavity designated generally as which comprises a generally cylindrical cathode section 11 and a generally cylindrical grid section 12. The cathode section 11 has an end wall 13 which supports a cathode heater 14 at its center. The heater is received in an indention 16 formed in the wall 13 and an emitting portion 17 covers the end of the indention 16 and is heated by a heater 14 to an electronemission temperature.

The grid structure 12 has an end wall 18 formed with a central opening 19 to allow electrons emitted from the cathode 17 to pass therethrough.

The cathode structure is insulated D.C. wise from the grid structure 12 by means of an insulating layer 21 which might be made of polystyrene, for example. Although the polystyrene placed between the overlapping portions of the cathode and grid forms a D.C. insulator,

'ice

it comprises substantially no reactance to an A.-C. signal so that grid 12 and cathode ljl-willzbe maintainedv atr A direct current bia-s Ecis' the same R.F. potential. maintained between the cathode 11 and the gridE 12 by connecting-a suitable D.C. source to the leads-22 and 23.

An inputcoupling loop 24 supplies inputY energy to the cavity resonator to excite it.

to McCreary and Harris, No. 2,641,733, which issued1 on J une 9, 3, for High Frequency Tube.

An output cavity designatedgenerally as 26l comprisesl a generally cylindrical portion' 27 which'has-.end wallsw 28 and 29.

Thebeam of electrons emitted from the inputl cavity 10 passes through .an-opening 31` formed in the end wall 2'8 and is receivedin a cup-'shaped collector 35:y A D.C.' accelerating voltage .Ebis maintained-between thel cathode 11 and the output cavity 26 sol thatv electron ow will occur between vthe input and output cavity. It isl to be noted lthat theopening 31 is offset from the'center of theV outputV cavity so that theV beam of-electrons emitted-from input cavity 10 enters and excites the output cavity aty ar relatively low voltage point.

Figure 2 illustrates the voltage distribution with-respect to the center of the outputtcavity. The'voltage'is defined:

by the equation l E =E]o(kr) sin wt where,

Jo is the zero order Bessel function of the first kind, k is the propagation constant,

r is the radial distance from the axis of symmetry of the j output cavity, w is the resonant angular frequency of the cavity, and tis the time.

Thus, it is seen that a much higher maximum voltage occurs at the center of the output cavity than occurs adjacent the edges. Since the beam from the input cavity 10 is fed to the output cavity 26 adjacent the outer edge, the voltage will be ampliiied to obtain a much higher voltage at the center.

An electron gun 32 has a heater 33 and `shoots a beam of electrons axially through the loutput cavity and out an `opening 34 formed in the end wall 29 to an output target 36. A probe 37 is mounted to extend within the output cavity and supplies an input to a phase control 38 which controls the output of electron gun 32. The phase control 38 has the characteristic that the electron gun 32 will produce an output only during the positive peaks of voltage.

The principal feature causing operation of the apparatus of this invention lies in the fact that a relatively large number of charged particles, or electrons, for cxample, give up their energy while traversing a small potential diiference in order to cause a smaller number of electrons to gain higher individual energy in traversing a large potential difference.

Thus, the input cavity 10 shoots electrons into the output cavity 26 and they give up their energy to the output cavity at a low voltage point. The electron gun 32 emits electrons into the cavity 26 at a time when they will be accelerated by the higher potential existing in the center of the cavity and the particles thus emitted will be ac- Y able vacuum chamber, as for example, a glass envelope.

`Patented, Aug. 13,-/ 1957 The envelope 40 is shown in the drawing and encloses the various parts of the device,

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be madetherein which are Within the full intended scope of the invention as defined by the appended claims. l

We claim:

l. Means for producing a stream of high energy charged particles comprising, an input cavity resonator formed with a generally cylindrical cathode section, a cylindrical grid section insulating material between said cathode and grid sections to insulate said sections from direct current, and a charged particle producing portion mounted within said input cavity resonator, an output cavity resonator of generally cylindrical shape and formed With an oit-center opening the imput cavity resonator in alignment with the olii-center opening, a second charged particle producing means mounted to the output cavity resonator, a phase control means connected to the second charged particle producing means to control it so that it emits charged particles only at a time when they will be accelerated, and a target in alignment with the second charged particle producing means and an envelope enclosing-the input cavity resonator, the output cavity resonator, and the target.

2. Means for iaccelerating charged particles to a high energy level comprising, an input cavity resonator, said input cavity resonator comprising a pair of hollow cupshaped members, insulating material between said cupshaped members to insulate them for direct current, a iirst electron gun mounted in the input cavity resonator, an opening formed in said input cavity resonator in axial alignment with said first electron gun, exciting means mounted within said input cavity resonator, an output 4 cavity resonator, a second electron gun mounted at a high voltage point of said output cavity resonator, an opening formed in said output cavity resonator at a low voltage point, said input cavity resonator mounted externally of said output cavity resonator and in alignment with the opening formed in said output cavity resonator, a phase control means connected to said second electron gun, and a pickup probe connected to said phase control and mounted within said output cavity resonator and an envelope enclosing the input and output cavity resonators.

3. Means for accelerating a charged particle comprising an input cavity resonator, a cathode section in said input cavity resonator, a grid section in said input cavity resonator, said grid section direct current insulated from said cathode section, an output cavity resonator, external input means individual to said cathode section, said grid section, and said output cavity resonator, an opening formed in said output cavity resonator in alignment with theinput cavity resonator with said opening formed at a low` voltage point, an electron gun mountedl within the input resonator at a high voltage point, said input cavity resonator mounted externally Vof the output cavity resonator, and an envelope enclosing the output and input cavity resonators. Y

References Citedin the le of this patent UNITED STATES PATENTS 

